Wet end disposition of latices on fibers

ABSTRACT

IN THE INCORPORATION OF LATEX INTO FIBERS IN WATER DISPERSION AND THE DEPOSITION OF POLYMERS THEREON BY COAGULATION WITH COAGULANTS, AN IMPROVED PROCESS AND PRODUCT ARE OBTAINED WHEN THERE IS ALSO ADDED LESS THAN 5 PARTS OF AN ANIONIC WATER SOLUBLE POLYMER SUCH AS POLYACRYLIC ACID PER 100 PARTS OF POLYMER IN THE LATEX.

United States Patent O 3,748,223 WET-END DISPOSITION OF LATICES N FIBERS Elmer R. Urig, 225 James Circle, Avon Lake, Ohio 44012 No Drawing. Continuation of abandoned application Ser.

No. 24,840, Apr. 1, 1970. This application Jan. 14,

1972, Ser. No. 218,016

Int. Cl. D21d 3/00 US. Cl. 162-169 10 Claims ABSTRACT OF THE DISCLOSURE In the incorporation of latex into fibers in water dispersion and the deposition of polymers thereon by coagulation with coagulants, an improved process and product are obtained when there is also added less than 5 parts of an anionic water soluble polymer such as polyacrylic acid per 100 parts of polymer in the latex.

This is a continuation of application Ser. No. 24,840 filed Apr. 1, 1970, now abandoned.

BACKGROUND OF THE INVENTION Latices have been used for years in impregnating fibrous materials including cellulosic fibers, asbestos, leather and other fibrous materials in wet form. A more recent and efficient method of incorporating synthetic polymers into such fibers, particularly paper, consists of wet-end or beater addition, that is defined to include methods of incorporating latex into, and deposition of polymers thereon, beaten pulp or fibers in water before sheet formation. Most commercial methods are based on coagulation of the latex by destabilization of the latex colloidal system by modification with additives such as papermakers alum.

With many latices, difficulties are experienced in obtaining complete deposition of the latex polymer particles onto the fibers, the resulting coagulum is often soft and causes sticking to Wire and felts, poorly adhered particles are dislodged during subsequent handling and reduce cross section uniformity and are lost in the white Water, and a cloudy serum or white water often containing both polymer and film fines that are undesirable is obtained. Improved methods for more completely depositing the polymer from latex onto wet fibers and a reduction in stickiness of the resulting product with clear serum is desired with use of minimum amounts of coagulants as alum. Excessive alum, for example, causes degradation of the resulting products.

SUMMARY OF THE INVENTION Use of less than 5 parts, as 0.01 to 3 parts, of an anionic water-soluble hydrophilic polymer and salts thereof such as polyacrylic acid, per 100 parts of polymer, with a polymer latex before addition to a dispersion of fibrous materials and precipitation or coagulation of the polymer with coagulants results in improved deposits of polymer particles onto the fibers to form deposited coagulum that does not cause sticking problems, decreases fines and provides clear white Water serum with the use of less alum than is required when the polyacrylic acid is not used. Further advantages include better retention of polymers in the fibers during additional processing, improved sheet formation, improved drainage rate of white water and improved physical properties of the resulting sheet.

DETAILED DESCRIPTION The incorporation of synthetic polymer latices into fibrous slurries or dispersions before formation of a sheet therefrom is termed wet-end or beater addition. This technique is used to incorporate in the fiber sheet from less than 1% to more than 50% polymer content, de-

3,748,223 Patented July 24, 1973 pending on the end use of the sheet. Controlled deposition of the latex particles is obtained by the addition of a coagulant such as papermakers alum in water solution. This improvement, use of anionic, water-soluble, hydrophilic polymers as polyacrylic acid, can be applied to a variety of techniques including direct addition, the inverted method, the Armstrong method, continuous addition, and the like.

In direct addition, after the furnish has been beaten to the desired degree of freeness, the pH of the pulp furnish is adjusted to between 8.5 and 9.0 with alkali. The latex is added to the pulp furnish and is dispersed by operating the beater. The latex may be diluted before addition. After the latex has been dispersed, a 1 to 10% solution of a coagulant, for example, alum, is added to coagulate the latex polymer which is deposited on the fibers. In the inverted method the furnish is beaten to the desired freeness, the pH is reduced to 4.5 using alum and dilute latex is added thereto. The Armstrong method is described in US. Pats. 2,375,245 and 2,613,190. In the continuous method the furnish is prepared, the pH reduced to 4.5 with alum and the latex is added after the furnish leaves the beater. It is understood by those skilled in the art that in commercial methods of latex wet-end addition, the latex is normally added as dilute as possible at a point of maximum agitation in the range of about 10 to T.S.

This invention may be applied to any synthetic polymer latex used in wet-end addition to fibrous slurries, and improvement will be obtained thereby both in the process and resulting sheet product, particularly in more complete deposition and clear serum. These include vinyl chloride, styrene, vinyl acetate, vinylidene chloride, acrylic ester, conjugated diene and like polymer latices, as is well known in the art, particularly latices of elastomeric polymers. Such latices include, for example, latices of alkyl acrylate polymers and copolymers, polychloroprene, copolymers of butadiene and acrylonitrile, butadiene and methyl methacrylate, butadiene and vinylidene chloride, butadiene and styrene, vinyl chloride polymer latices including copolymers of vinyl chloride and 5 to 40 parts of copolymerized alkyl acrylates and the like. Typical useful latices are described in Synthetic Rubber, Whitby, 1954 and Polymer Processes, Schildknecht, 1956.

This invention is particularly adapted to use of latices containing polymers of alkyl acrylates. Alkyl acrylate polymers are valuable in providing improved fibrous articles containing the alkyl acrylate polymers dispersed thereon. Since some alkyl acrylates have some water solubility, polymerization thereof to form latices may be conducted in the presence of minimum amounts of surface active agents. More difliculty has been experienced in adequately depositing low surface active-containing or nonionic emulsifier-containing latices on fibrous materials in aqueous suspension than with latices containing 1 larger amounts of ionic surface active agents. Such polymers include homoand copolymers of alkyl acrylates wherein the alkyl groups of esters of acrylic acid contain from 1 to 8 carbon atoms. Improved polymer latices are prepared from copolymers of alkyl acrylates with vinylidene monomers containing terminal CH groups; including particularly, monomers such as styrene, a-methyl styrene, acrylonitrile, methacrylonitrile, ethyl methacrylate, butyl methacrylate, methyl ethacrylate, vinyl chloride, vinylidene chloride, vinyl acetate and the like. Such polymers may also include cure sites generally supplied by chlorine-containing monomers as vinyl chloroacetate, chloropropyl acrylate, chloroethyl vinyl ether, and other known comonomers.

Excellent results have been obtained with latices of alkyl acrylates containing as much as 20% of reactive monomers, for example, acrylamide and methacrylamide,

t-butyl acrylamide, octyl acrylamide and diacetone acrylamide, N-alkylol amides as N-methylol acrylamide and N-methylol methacrylamide, N-alkoxyalkyl acrylamides including for example, N-ethoxy methacrylamide and N- butoxy methacrylamide, ugh-unsaturated carboxylic acids containing 3 to 8 carbon atoms including, for example, acrylic acid and methacrylic acid, dicarboxylic acids as itaconic acid, and the like. Normally, at least about 0.2% of these comonomers are used. Useful are copolymers of ethyl, methyl and lbutyl acrylate containing about one part each of at least two such comonomers for example, N-butoxymethyl acrylamide and acrylarnide, N-methylol acrylamide and acrylamide, N-methylol acrylamide and methacrylamide, N-methylol acrylamide and acrylic acid and the like. The total of such monomers normally being less than about 10% of the copolymer.

The polyacrylic acid should have a molecular weight greater than about 2,000 and may be as high as about 3,000,000. Polymers of average number molecular weights of about 10,000 to 300,000 normally will be used. The polyacrylic acid is used in amounts less than about parts per 100 parts of polymer in the latex. Usually no more than about 1 weight part per 100 weight parts of latex polymer is required. Excellent results have been obtained when the concentration is about 0.1-0.5 part. While amounts as low as 0.001 to 0.01 show improved results, larger amounts usually provide better results both in the process and resulting product. Other polymeric afi-aCidS may be used so long as they are water-soluble including, for example, polymethacrylic acid, polyitaconic acid and the like. Copolymers of such acids also may be used so long as the copolymer is water soluble. The polyacrylic acid may be added in the latex. It may be present during polymerization of the latex monomers.

While polyacrylic acid, or alkali metal water-soluble salts thereof as sodium polyacrylate, is the preferred anionic, water-soluble, hydrophilic polymer for use in this invention, improved results have been obtained with carboxymethyl cellulose, casein, alginates, poly(methacrylamide) and the like.

The coagulants used in addition to the preferred alum include water-soluble polyvalent metal salts used in the art such as potassium sulfate, magnesium sulfate and the like.

To demonstrate the advantages of the invention, 400 ml. of 1% bleached Kraft furnish was placed in a container and agitated with a mixer at high speed. 3 ml. of latex was added slowly to the furnish. Sufi'jcient 5% alum solution was added slowly to cause coagulation. The mixture was stirred for minutes and a sheet formed therefrom and the drainage rate measured.

A series of synthetic polymer latices was tested by this technique including (1) 50% total solids latex of polyethyl acrylate containing 5% of a nonionic surface active agent, polyoxyethylene nonyl phenol ether, (2) a 38% total solids latex of a copolymer of about 66% butadiene and 33% acrylonitrile with 5 parts of rosin acid soap emulsifier, (3) a 35% total solids latex of a similar copolymer of (2) also containing 3 parts methacrylic acid and 1 part of N-methylol acrylamide with 5 parts of sodium alkylnaphthalene sulfonate, (4) 50% total solids latex of a copolymer of ethyl acrylate, 1 part of acrylic acid and 3 parts of N-methylol acrylamide with 6 parts of sodium lauryl sulfate, (5) a 50% total solids latex of a coplymer of about 90 parts of vinyl chloride and 10 parts of ethyl acrylate with about 5 parts of sodium alkylnaphthalene sulfonate, (6) 20% total solids of a latex of a copolymer of about 75% butadiene and 25% styrene with 5 parts of fatty acid soap.

With (1), when 5% alum solution was added to cause precipitation the resulting coagulum was soft, there were polymer fines in the water and the white water was cloudy. With this latex containing 0.1 part of polyacrylic acid, 50% less alum solution was required to cause precipitation, the resulting coagulum was firm and the white water was clear.

With (2), the white water contained polymer fines and was cloudy. With this latex containing 0.1 part polyacrylic acid, 25% less alum solution was required to cause coagulation. The coagulum was firm and the white water was clear.

With (3), the white water contaned polymer fines and was cloudy. With this latex containing 0.1 part polyacrylis acid, 25% less alum solution was required to cause coagulation. The coagulum was firm and the white water was clear.

With (4), when 5% alum solution was added to cause precipitation the resulting coagulum was soft, there were polymer fines in the water, and the white water was cloudy. With the latex containing 0.1 part of polyacrylic acid, 30% less alum solution was required to cause precipitation, the resulting coagulum was firm and the white water was clear.

With (5), the coagulum was soft, the white water contained polymer fines and was cloudy. With the latex containing 0.1 part polyacrylic acid, 25% less alum solution was required to cause coagulation. The coagulum was firm and the White water was clear.

With (6), the white water contained polymer fines and was cloudy. With the latex containing 0.1 part polyacrylic acid 25 less alum solution was required to cause coagulation. The coagulum was firm and the white Water was clear.

In each case the sheet formed from latex not containing a polyacrylic acid was more tacky and sticky than that from latex containing the polyacrylic acid and could cause some screen and felt sticking. All the polymer was not completely deposited on the fibers and some that was deposited came loose and appeared as fines in the white water serum which was not the case when the latices contained polyacrylic acid. In coagulation with alum in the absence of the polyacrylic acid, some polymer particles that are deposited are not adequately bound to the fibers and may be dislodged during handling operations and these unattached polymer particles reduce sheet cross section uniformity. The resultant polymer loss into the white water requires additional treating steps and is uneconomical. Improved drainage of the sheets also is noted when latices containing polyacrylic acid are used. Even better results are observed when more dilute latex is used.

Thus, the use of polyacrylic acid provides an improved process where less alum is required, improved coagulum with better retention on fiber is obtained, polymer fines are reduced and clear white water is obtained that can be reused without costly treatment. Process advantages when the sheets are less tacky are also observed.

Paper sheet formed in accordance with this invention with the above latex composition have good appearance, improved drainage rate, there is no sticking to screen or felt; the dry sheets have no oil-color spots, good reflectance, percent elongation and tensile strength. Sheets prepared from the same latices and by the same process Without the polyacrylic acid or salt thereof had longer drainage rates, scum on the sheets and the sheets have a grainy appearance, some slight sticking to the screen and some had off-color spots. The major advantages of the invention are in improved processing, requiring less coagulant or alum, better deposition of polymer to fibers and clear serum.

I claim:

1. In the process for preparing fiber sheets having polymer latex particles deposited on the fibers wherein synthetic polymeric latices are added to fiber slurries or dispersion by the wet-end addition before formation of a sheet therefrom by coagulation, the improvement comprising adding to said dispersion before coagulation 0.1 to less than 5 parts per weight parts of latex polymer of an anionic water-soluble hydrophilic polymer having a molecular weight greater than about 2000 selected from the group consisting of polyacrylic acid, polymethacrylic acid, polyitaconic acid and alkali metal water-soluble salts thereof.

2. The process of claim 1 wherein the water-soluble polymer is polyacrylic acid in amounts from about 0.1 to 3 parts.

3. The process of claim 2 wherein the latex contains a polymer of an alkyl acrylate.

4. The process of claim 3 wherein the alkyl acrylate polymer contains less than 20% of an acrylamide.

5. The process of claim 2 wherein the latex contains a butadiene polymer.

6. The process of claim 5 wherein the polymer is a copolymer of butadiene and acrylonitrile.

7. The process of claim 5 wherein the polymer is a copolymer of butadiene and styrene.

8. The process of claim 2 wherein the latex contains polychloroprene.

9. The process of claim 4 wherein the alkyl acrylate is ethyl acrylate.

10. The process of claim 2 wherein the latex contains a copolymer of vinyl chloride.

References Cited UNITED STATES PATENTS 2,880,090 3/1959 Feigley 16216 9 2,868,641 l/l959 Feigley 162169 X 3,193,446 7/1965 Eisenberg l62l83 X 3,232,824 2/ 1966 Bader 162169 ROBERT L. LINDSAY, 111., Primary Examiner U.S. Cl. X.R. 

